1. Field of the Invention
The subject invention relates to an improved heater for a corrugating machine and, in particular, to a heater for imparting heat to the medium paper.
2. Description of the Prior Art
It is well known in the art to produce corrugated flutes from a flat sheet of paper medium by feeding the flat sheet through two meshing corrugating rolls, where the two rolls have teeth appropriately configured for the requisite flutes on the paper. Prior to feeding the paper into the corrugating rolls, the paper must be conditioned for the reconfiguration, such conditioning typically including both heating and steaming of the paper.
To preheat the paper, a steam pressurized drum heater is typically provided, and operated with steam in the range of 370.degree. F. at 185 psig. The paper is wrapped around the circumference of the drum and the heat from the surface of the drum is transferred to the moving paper. From the drum heater, the paper is fed over a steam chamber, where steam is imparted directly to the paper to loosen the paper fibers, such that the fibers are pliable and more easily formed.
One of the disadvantages to the present heating system is that due to the large internal void created within the drum, and the conditions under which the drum operates, the heating drum must be qualified as a "pressure vessel" under the ASME pressure vessel code. Due to this qualification, the heating drum must include relatively thick walls reducing the maximum possible heat transfer rate from the heating surface to the paper.
Another disadvantage to the drum heater as described above is that due to the thermal inefficiency, the drum must be made relatively large in size, typically in the range of 24 inches in diameter. The drum heater must therefore be placed, exterior to, and typically behind, the corrugating apparatus. Due to this position, there is a considerable distance between the heating drum and the steam chamber, and the paper is cooled during the travel between the heating drum and the steam chamber, thereby further reducing the overall thermal efficiency of this process.
It is an object of the invention then to design a corrugating apparatus and preheater where the thermal efficiency of the overall process is improved.
It is a further object of the invention to design a heater for a corrugating apparatus which allows for an overall compact design of the corrugating apparatus.
It is a further object of the invention to provide for a means to vary the angle of wrap on the preheater to vary the heat transfer for various operating conditions and paper thicknesses, without significantly increasing the tension on the paper due to the frictional force across the heater.